Melanomas are aggressive, frequently metastatic tumors derived from either melanocytes or melanocyte related nevus cells (“Cellular and Molecular Immunology” (1991) (eds) Abbas A. K., Lechtman, A. H., Pober, J. S.; W.B. Saunders Company, Philadelphia: pages 340-341). Melanomas make up approximately three percent of all skin cancers and the worldwide increase in melanoma is unsurpassed by any other neoplasm, with the exception of lung cancer in women (“Cellular and Molecular Immunology” (1991) (eds) Abbas, A. K., Lechtiman, A. H., Pober, J. S.; W.B. Saunders Company Philadelphia pages: 340-342; Kirkwood and Agarwala, (1993) Principles and Practice of Oncology 7:1-16). Even when melanoma is apparently localized to the skin, up to 30% of the patients will develop systemic metastasis and the majority will die (Kirkwood and Agarwala, (1993) Principles and Practice of Oncology 7:1-16). Classic modalities of treating melanoma include surgery, radiation and chemotherapy. In the past decade immunotherapy and gene therapy have emerged as new and promising methods for treating melanoma.
T cells play an important role in tumor regression in most murine tumor models. Tumor infiltrating lymphocytes (TIL) that recognize unique cancer antigens can be isolated from many murine tumors. The adoptive transfer of these TIL plus interleukin-2 can mediate the regression of established lung and liver metastases (Rosenberg, S. A., et al., (1986) Science 233:1318-1321). In addition, the secretion of IFN-γ by injected TIL significantly correlates with in vivo regression of murine tumors, suggesting activation of T cells by the tumor antigens (Barth, R. J., et al., (1991) J. Exp. Med. 173:647-658). The known ability of tumor TIL to mediate the regression of metastatic cancer in 35 to 40% of melanoma patients when adoptively transferred into patients with metastatic melanoma attests to the clinical importance of the antigens recognized (Rosenberg, S. A., et al., (1988) N. Engl. J. Med. 319:1676-1680; Rosenberg, S. A., (1992) J. Clin. Oncol. 10:180-199).
T cell receptors on CD8+ T cells recognize a complex consisting of an antigenic peptide (9-10 amino acids for HLA-A2), β-2 microglobulin and class I major histocompatibility complex (MHC) heavy chain (HLA-A, B, C, in humans). Peptides generated by digestion of endogenously synthesized proteins are transported into the endoplastic reticulum, bound to class I MHC heavy chain and β2 microglobulin, and finally expressed in the cell surface in the groove of the class I MHC molecule. Thus, T cells can detect molecules that originate from proteins inside cells, in contrast to antibodies that detect intact molecules expressed on the cell surface. Therefore, antigens recognized by T cells may be more useful than antigens recognized by antibodies.
Although emphasis is on CD8+ T cell responses, there is emerging support that CD4+ T cells may play an important role in anti-tumor immunity. As reviewed by Pardoll and Topalian (Curr. Opin. Immunol. 10:588, 1998), CD4+ T cells have been demonstrated in murine studies to exert helper activity through the induction of CD8+ T cells and B cells and further have both direct and indirect effects on tumor cells, including those deficient in MHC class II. In humans, CD4+ T cells play a critical role in the initiation of several autoimmune diseases (Parry et al., Curr. Opin. Immunol. 10:663, 1998) and in pathogenic resistance (Mata and Paterson, J. Immunol. 163:1449, 1999; Zajac et al., J. Exp. Med. 188:2205, 1998). CD4+ T cells activated dendritic cells primarily through the interaction of CD40 and its ligand. There is growing support that the combination of MHC class I and class II epitopes derived from the same tumor antigen can enhance antitumor effector function and long-term immunity (Surman et al., J. Immunol. 164:562, 2000; Ossendorp et al., J. Exp. Med. 187:693, 1998; Matloubian et al., J. Virol. 68:8056, 1994).
Strong evidence that an immune response to cancer exists in humans is provided by the existence of lymphocytes within melanoma deposits. These lymphocytes, when isolated, are capable of recognizing specific tumor antigens on autologous and allogeneic melanomas in an MHC-restricted fashion (Itoh, K. et al. (1986), Cancer Res. 46: 3011-3017; Muul, L. M., et al. (1987), J. Immunol. 138:989-995); Topalian, S. L., et al., (1989) J. Immunol. 142: 3714-3725; Darrow, T. L., et al., (1989) J. Immunol. 142: 3329-3335; Hom, S. S., et al., (1991) J. Immunother. 10:153-164; Kawakami, Y., et al., (1992) J. Immunol. 148: 638-643; Hom, S. S., et al., (1993) J. Immunother. 13:18-30; and O'Neil, B. H., et al., (1993) J. Immunol. 151: 1410-1418). TIL from patients with metastatic melanoma recognize shared antigens including melanocyte-melanoma lineage specific tissue antigens in vitro (Kawakami, Y., et al., (1993) J. Immunother. 14: 88-93; Anichini, A. et al., (1993) et al., J. Exp. Med. 177: 989-998). Anti-melanoma T cells appear to be enriched in TIL, probably as a consequence of clonal expansion and accumulation at the tumor site in vivo (Sensi, M., et al., (1993) J. Exp. Med. 178:1231-1246). The fact that many melanoma patients mount cellular and humoral responses against these tumors and that melanomas express both MHC antigens and tumor associated antigens (TAA) suggests that identification and characterization of additional melanoma antigens will be important for immunotherapy, of patients with melanoma.
The melanocyte differentiation antigen, gp100, is expressed in more than 75% of human melanomas (Cormier et al., Int. J. Cancer 75:517, 1998). Although the gp100 antigen is predominantly expressed intracellularly, it is a suitable immunogenic antigen. The intracellular proteins have been demonstrated to be processed and presented as peptides in the context of MHC molecules to immune system cells. In particular, TIL derived from tumors of melanoma patients have been identified and react with the gp100 antigen. Given that vaccination with a modified gp100 CD8+ T cell epitope combined with IL-2 reportedly resulted in a 42% response rate in patients with metastatic melanoma (Rosenberg et al., Nat. Med. 4:321, 1998; Parkhurst et al., J. Immunol. 157:2539, 1996), only a few patients responded clinically to this particular vaccine regimen, and additionally, only transient responses were observed. Thus, in order to increase the immunogenicity and therapeutic efficacy of vaccines comprising gp100 CD8+ T cell epitopes, antigen-specific CD4+ T cells can be combined. Therefore, the gp100 MHC class I and class II epitopes can be useful for cellular responses against melanoma, and can also play a significant role in therapy and diagnosis of melanoma patients.
Peripheral blood lymphocytes have been used to identify several potential melanoma tumor antigens. For example, Van Der Bruggen et al. (Science 254: 1643-1647, 1991) has characterized a gene coding for a melanoma antigen, designated MAGE-1, using T cell clones established from the peripheral blood of patients who were repetitively immunized in vivo with mutagenized tumor cells. Cytotoxic T cells derived from the peripheral blood lymphocytes of patients with melanoma were used to identify a potential antigenic peptide encoding MAGE-1 (Traversari, C., et al. (1992) J. Exp. Med. 176:1453-1457). Brichard et al. ((1993) J. Exp. Med. 178:489-495) has also characterized a gene encoding a melanoma antigen designated tyrosinase using peripheral blood lymphocytes from patients who were sensitized by repetitive in vitro stimulation with tumor. Further support for the therapeutic potential of melanoma antigens is provided by Brown et al. (U.S. Pat. No. 5,262,177). Brown et al. (U.S. Pat. No. 5,262,177) relates to a recombinant vaccinia virus-based melanoma vaccine where the melanoma antigen p97 is reported to show a protective effect from tumor cell challenge in a murine model. Characterization of additional melanoma antigens can be important for the development of new strategies for cancer immunotherapy, in particular for melanoma.